This invention relates generally to a fluid cylinder such as a hydraulic or a pneumatic cylinder or the like, and more particularly, to a fluid cylinder including an embedded sensor and sensor electronics module for determining positional information for a rod of the cylinder.
Known linkage systems utilizing fluid cylinders for changing link length and angular orientation typically utilize controls wherein information relating to the length and/or velocity of movement of one or more cylinder rods is required. The electrical aspects of control apparatus for such systems typically require the use of a variety of sensors, including, but not limited to, lever position sensors and linkage position sensors, and also utilize electro-hydraulic valves and an onboard electronic control module operable for executing a control strategy for linkage movement. A central portion of such control strategies is typically a linkage position input which can be embodied, for instance, in positional and/or velocity information for a cylinder rod. Such positional and velocity information is typically collected by a position sensor mounted on or in a subject fluid cylinder or on a linkage and through the linkage kinematics one can translate linkage angle into cylinder length. Reliable data collection from such sensors has been found to be largely dependent on the ability to maintain the integrity of such sensors and the conductive element or other path of communication between the sensor and the system under adverse operating and environmental conditions, such as heat, cold, dust, dirt, and contact with rocks and other objects that can damage the sensor and/or its path of communication with other elements of the control system.
Currently, to reduce the potential for damage to sensors from such operating and environmental factors, the sensors themselves are sometimes located within the cylinder housing or body. Reference in this regard, Chan et al. U.S. Pat. No. 5,977,778 issued Nov. 2, 1999 to Case Corporation of Racine, Wisconsin, which discloses a method and apparatus for sensing piston position including a transmitter/receiver unit mounted on a cylinder housing in communication with an internal cavity thereof for sensing position of a piston of the cylinder and communicating via a conductive path to circuitry located externally to the cylinder for processing the signal data and generating an output signal representative of the piston position. Reference also Tellerman U.S. Pat. No. 4,952,873 issued Aug. 28, 1990 to MTS Systems Corporation of Eden Prairie, Minn. which discloses a compact head, signal enhancing magnetostrictive transducer mounted on a mounting head positionable in a tank, cylinder or the like for sensing a piston position or liquid level, which transducer is connected via one or more conductive paths to electronic circuitry for providing output signals indicative of a displacement. However, known systems such as these have been found to provide only a partial solution to the problems encountered as electronic components required for the operation of the sensors and transducers thereof are still located externally to the cylinder so as to still be subjected to the adverse operating and environmental factors.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, a fluid cylinder is disclosed which includes a cylinder body including a cylindrical internal cavity therein having a longitudinal axis therethrough, the internal cavity being adapted for disposition of a piston and rod assembly for axial movement therein. The cylinder includes a member such as an end cap enclosing an axial end of the internal cavity, the member having a sensor port or passage therethrough extending between an internal opening communicating with the internal cavity and an external opening, a sensor disposed in the internal opening of the sensor port, and a sensor electronics module disposed in the sensor port between the sensor and the external opening, the sensor being connected to the sensor electronics module by a conductive element and being operable for sensing an axial distance of the piston or the rod from the sensor or a predetermined location and outputting signals representative of the distance along the conductive element to the sensor electronics module, the sensor electronics module including circuitry for receiving the signals, determining an axial position of the piston or the rod from the signals, and outputting a position signal representative of the axial position of the piston or the rod.
In one preferred aspect of the invention, the sensor is a magnetostrictive type sensor and includes a pressure pipe extending into the internal cavity in position to be cooperatively received telescopically within an axial passage extending into or through the rod. According to another preferred embodiment of the invention, the internal opening of the sensor port includes a central portion which is offset radially from the axis of the internal cavity and the pressure pipe has a longitudinal axis which is offset from a central portion of the sensor such that the pressure pipe is coaxial with the cavity and can be received in the passage of the rod. Additionally, the end cap member of the cylinder includes a fluid port extending therethrough to an axially facing opening beside the internal opening of the sensor port.
According to another preferred aspect of the invention, the sensor electronics module and the sensor, with the exception of the magnetostrictive element located in the pressure pipe, are contained within a unitary sensor housing. Alternatively, the sensor electronics module can be separately housed and located in or adjacent the external opening of the sensor port to facilitate removal and replacement.